This invention relates to a process for treating radioactive waste gases, more particularly to a process for recovering radioactive rare gases from the waste gas of a nuclear power plant.
Apparatus as shown in FIG. 1 has been used to treat the waste gas from a nuclear power plant to recover radioactive rare waste gases. According to this method, the waste gas is pretreated in a pretreating system 1 to remove water and carbon dioxide gas and is then cooled in a heat exchanger 2 by effluent gas from a concentrator 4. Thereafter, the cooled gas is sent to a primary condenser 4 which usually comprises a low temperature adsorption bed cooled by the liquid nitrogen from a tank 3. In the primary condenser the waste gas is concentrated by a factor of about 5000, the concentrated gas consisting of a major proportion of air (N.sub.2, O.sub.2, etc.) and about 1/10th of rare gases, for example, (Xe, Kr, etc.). The concentrated waste gas is sent by a pump 5 to a secondary condenser 6 where the radioactive rare gases are adsorbed by an activated carbon bed and then recovered in tank 7.
Where an activated carbon bed is used in the secondary condenser, a certain amount of oxygen is also adsorbed along with the rare gases. The adsorbed oxygen is activated by the radioactivity of the radioactive rare gases and a portion thereof is converted into ozone. Since ozone is explosive, it is dangerous to recover it in tank 7 along with the rare gases. Further, the activated carbon of the bed is burnt and wasted by the heat of disintegration or heat of reaction of ozone thereby greatly decreasing the absorption capability of the activated carbon.
Because of the above noted problems, it is desirable to remove oxygen admixed with the radioactive rare gases before recovering the same.
Accordingly, a method has been proposed wherein a H.sub.2 -O.sub.2 recombiner is used in the secondary condenser 6 instead of a low temperature absorption bed. According to this method, hydrogen gas is blown into the condenser for reaction with the oxygen. This method is advantageous for the secondary condenser because oxygen is substantially completely removed. However, it has a defect that it is necessary to install a hydrogen tank or a hydrogen generating device near the radioactive rare gas recovering system, thereby increasing the possibility of an explosion of the hydrogen, resulting in an extremely dangerous situation.